1. Field of the Invention
The present invention relates to an automatic system for preventing external cargo spillage from tanker vessels resulting from the overflow of cargo from the cargo compartments of the vessel during loading thereof.
2. Description of the Prior Art
Presently, cargo comprising fluid chemical and petroleum products, such as, for example, oil, is loaded into tanker vessels by means of transfer hoses and cargo pipelines which are coupled to inlets communicative with the cargo compartments of the vessel. It sometimes occurs during loading or transfer of cargo that the fluid and chemical products continue to flow after the compartments are full. As a result, cargo overflows through ullage openings, gas vents or other deck apertures communicative with the compartments, over the deck of the vessel and into the water, thereby causing a spill and producing water contamination, atmospheric pollution, as well as a fire and explosion hazard.
Cargo spills are the result of a variety of causes. One, for example, is negligence on the part of personnel in charge of loading the cargo compartments of the vessel. Another is a faulty loading valve, for example, a leaky valve or a foreign substance wedged under the valve gate. Others are a leaking line under pressure within the cargo compartments; an increase, without notice, of the vessel loading rate; and a broken valve reach rod or other control segment during closing of an inlet valve after a cargo compartment has been filled. Such cargo overflows can cause significant pollution of coastal waterways, particularly when the cargo being loaded is crude oil. For example, depending upon the size of the vessel and the flow rate of the cargo during loading and the duration of the overflow before it is discovered, anywhere from several barrels to several thousand barrels of oil may be lost from a single cargo spill caused by an overflow.
Cargo tank overfill control systems have been devised to prevent overflows from cargo compartments of a tanker vessel during loading. High level alarms and continuous tank cargo level indicators, for example, are used to monitor cargo tank levels in a vessel during loading. While such devices are helpful, they are subject to malfunctions, are dependent on human monitors, and do not automatically prevent pollution, and these characteristics make such devices unacceptable for vessels carrying cargoes such as crude oil having the potential of creating serious environmental pollution in coastal waterways and ports in the event of spillage from the vessel caused by an overflow during loading. Remotely-actuated, quick-closing shut off valves have been used in such vessels to help reduce overflows but it has been found that such valves can create excessive surge pressures in the cargo transfer hoses and pipelines used to load the vessel which are great enough to rupture the hoses and line thereby resulting in the spillage of cargo. Such valves are, moreover, still dependent on human attention for effective operation.